Hybrid-electric and pure electric vehicles rely on a traction battery to provide power for propulsion. To ensure optimal operation of the vehicle, various properties of the traction battery may be monitored. One useful property is the battery power capability which indicates how much power the battery may supply or absorb at a given time. Another useful property is the battery state of charge which indicates the amount of charge stored in the battery. The battery properties may be important for controlling operation of the battery during charging/discharging, maintaining the battery within operating limits, and balancing cells of the battery.